Since the mid-1980s metallocene catalysts have been used in high-pressure reactors—mainly for producing ethylene-backbone polymers including ethylene copolymers with monomers of one or more of propylene, butene, and hexene, along with other specialty monomers such as 4-methyl-1,5-hexadiene. For example, U.S. Pat. No. 5,756,608 to Langhausen et al., reports a process for polymerizing C2 to C10 1-alkenes using bridged metallocene catalysts. Polypropylene production in high pressure conditions has, however, been seen as impractical and unworkable at temperatures much above the propylene critical point. A process to produce commercially useful polypropylene in a high pressure system would provide advantages, such as increased reactivity, or increased catalyst productivity, or higher throughput, or shorter residence times, etc. Likewise new polypropylene polymers are also in constant need for the preparation of new and improved products. Thus there is a need in the art to develop new processes capable of greater efficiency and manufacture of new polypropylene polymers.
In addition there is also a need for polymerization processes that are flexible enough to be used with other monomers. For example, a high pressure process to make polybutene or polyhexene is also desirable.
U.S. Pat. No. 6,084,041, granted to Andtsjö et al., discloses supercritical propylene polymerization under relatively mild conditions (90-100° C. and less than 6.89 MPa pressure) using supported Ziegler-Natta and metallocene catalysts. This patent does not relate to propylene copolymerization at temperatures or pressures much higher than described above. It also does not specifically disclose bulk propylene polymerization using soluble, unsupported metallocene catalysts.
U.S. Pat. No. 5,969,062 granted to Mole et al., describes a process for preparing ethylene copolymers with α-olefins in which polymerization is carried out at a pressure between 100-350 MPa and at a temperature from 200-280° C. The catalyst is based on a tetramethylcyclopentadienyl titanium complex.
U.S. Pat. No. 5,408,017 describes an olefin polymerization catalyst for use at polymerization temperatures of 140° C.-160° C., or greater. Mainly, temperatures exceeding the melting point temperature and approaching the polymer decomposition temperature are said to yield high productivity.
WO 93/11171 discloses a polyolefin production process that comprises continuously feeding olefin monomer and a metallocene catalyst system into a reactor. The monomer is continuously polymerized to provide a monomer-polymer mixture. Reaction conditions keep this mixture at a pressure below the system's cloud-point pressure. These conditions create a polymer-rich and a monomer-rich phase and maintain the mixture's temperature above the polymer's melting point.
U.S. Pat. No. 6,355,741 discloses a process for producing polyolefins having a bimodal molecular weight distribution. The process comprises producing a first polyolefin fraction in a first loop reactor. The process couples this first loop reactor to a second loop reactor that prepares a second polyolefin fraction. At least one of the loops uses supercritical conditions.
WO 92/14766 describes a process comprising the steps of (a) continuously feeding olefinic monomer and a catalyst system, with a metallocene component and a cocatalyst component, to the reactor; (b) continuously polymerizing that monomer in a polymerization zone reactor under elevated pressure; (c) continuously removing the polymer/monomer mixture from the reactor; (d) continuously separating monomer from molten polymer; (e) reducing pressure to form a monomer-rich and a polymer-rich phase; and (f) separating monomer from the reactor.
U.S. Pat. No. 5,326,835 describes bimodal polyethylene production. This invention's first reactor stage is a loop reactor in which polymerization occurs in an inert, low-boiling hydrocarbon. After the loop reactor, the reaction medium transits into a gas-phase reactor where gas-phase ethylene polymerization occurs. The polymer produced appears to have a bimodal molecular weight distribution.
CA 2,118,711 (equivalent to DE 4,130,299) describes propylene polymerization at 149° C. and 1510 bar using (CH3)2C(fluorenyl)(cyclopentadienyl) zirconium dichloride complex, methylalumoxane and trimethylaluminum. Catalyst activity is reported to be 8380 gPP/g Ic′ h. The Mw is reported to be 2,000. CA 2,118,711 also describes propylene polymerization with ethylene at 190° C. and 1508 bar using (CH3)2C(fluorenyl)(cyclopentadienyl)zirconium dichloride complex, methylalumoxane and trimethylaluminum. Catalyst activity is reported to be 24358 g Polymer/gIc′ hr. The Mw is reported to be 10,000.
WO 2004/026921 discloses a process to polymerize olefins comprising contacting, in a polymerization system, olefins having three or more carbon atoms with a catalyst compound (such as a metallocene), activator, optionally comonomer, and optionally diluent or solvent, at a temperature above the cloud point temperature of the polymerization system and a pressure no lower than 10 MPa below the cloud point pressure of the polymerization system, where the polymerization system comprises any comonomer present, any diluent or solvent present, the polymer product, where the olefins having three or more carbon atoms are present at 40 weight % or more.
Furthermore, various processes and catalysts exist for the homopolymerization or copolymerization of unsaturated monomers, particularly the polymerization of olefins. For many applications, it is desirable for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. Chiral bis-indenyl metallocene catalysts have been used to prepare highly crystalline isotatic polypropylene and copolymers of propylene and other monomers (Resconi, L. Chem. Rev. 2000, 100, 1253). Non-chiral metallocene catalysts have also been prepared which yield atactic polypropylene and copolymers (Resconi, L. in Metallocene Based Polyolefins, Eds. J. Schiers, W. Kaminsky; Wiley; NY, 2000; 467). While there are chiral catalysts which operate between these extremes, yielding polypropylene with crystallinity less than highly crystalline and more than amorphous, generally these chiral catalysts give low molecular weight polymer. This is also true for copolymers prepared from propylene and other monomers, using such systems.
U.S. Pat. No. 6,051,522 describes bridged chiral metallocenes as catalysts useful for olefin polymerization. WO 2002/01745, U.S. 2002/0004575A1, WO 2002/083753A1, and U.S. Pat. No. 6,525,157 disclose processes for the preparation of a propylene/ethylene copolymer containing tacticity within the propylene sequences using the chiral metallocene rac-Me2Si(1-indenyl)2HfMe2 and an ionizing activator. U.S. Pat. No. 6,057,408 discloses a process for the preparation of high molecular weight propylene/ethylene copolymers with high crystallinity in the propylene sequences using chiral bis-indenyl metallocenes. The catalyst that yielded the highest molecular weight copolymer was rac-Me2Si(2-Me-4-(1-napthyl)-1-indenyl)2ZrCl2.
S. Collins and coworkers reported (Organometallics 1992, 11, 2115) a study of the effect of substituents in the 5,6-positions on a series of chiral ethylene bridged metallocenes, rac-(CH2CH2)(5,6-X2-1-indenyl)2ZrCl2, on solution ethylene and propylene polymerizations. In comparing X=H and X=Me, similar molecular weights were found for the preparation of polyethylene (X=H, Mn=145 kg/mol; X=Me, Mn=127 kg/mol) and polypropylene (X=H, Mn=15.7 kg/mol; X=Me, Mn=16 kg/mol). Likewise, in U.S. Pat. No. 5,455,365, chiral bis-indenyl metallocenes containing methyl groups in the 5 and 6 positions and metallocenes containing a phenyl group in the 5 or 6 position are disclosed. Polymerizations at 70° C. in liquid propylene gave moderately crystalline polypropylene, as evidenced by polymer melting points between 132 and 147° C. The molecular weights (Mw) of these materials are between 100 and 200 kg/mol. Copolymerization of propylene with ethylene, using rac-Me2Si(2,5,6-Me3-1-indenyl)ZrCl2/MAO, yielded a 2.8 wt % ethylene, 97.2 wt % propylene copolymer with a significantly lower molecular weight as evidenced by a drop in intrinsic viscosity from 155 mL/g (Mw=143 kg/mol) to 98 mL/g (Mw not recorded). This copolymerization also gave a decrease in melting point from 132 to 123° C.
In U.S. Pat. No. 6,084,115, a chiral bis-indenyl metallocene containing an annulated tetramethylated cyclohexyl ring attached at the 5 and 6 positions is disclosed. This metallocene, rac-Me2Si(5,6,7,8-tetrahydro-2,5,5,8,8-pentamethyl-benz[f]indenyl)2Zr(1,4-diphenylbutadiene), is reported to be in the +2 oxidation state. Propylene polymerization behavior was reported in alkane solution (24 wt % propylene) under a partial pressure of hydrogen at 70° C. Molecular weights obtained were ca. 60 kg/mol and polymer melting points were 144.8-147° C. These molecular weights were lower than the analogous complex with H in the 5 and 6 positions, rac-Me2Si(2-Me-1-indenyl)Zr(1,4-diphenylbutadiene), Mw=79 kg/mol. Similar results were observed in ethylene/octene polymerizations with these two catalysts. No H2-free solution polymerizations were reported. Supported catalysts were also examined in U.S. Pat. No. 6,084,115, however broad molecular weight distributions (>3.5) make comparisons between catalysts difficult. These results indicate that a molecular weight advantage is not expected for catalysts with large groups in the 5 and 6 positions. Thus, no meaningful increase in polymer molecular weight can be ascribed to these previous substitutions.
WO 2004/050724 discloses polymerization of butene with methylalumoxane and dimethylsilyl bis[2-methyl-5,6(tetramethyl-cyclotrimethylen)indenyl]zirconium dichloride and also described certain indenyl type compounds with annulated six membered rings; however, WO 2004/050724 does not obtain higher molecular weights at higher temperatures.
Thus there is a need in the art to provide catalyst systems that can provide polymers having high molecular weight as well as good crystallinity preferably prepared at higher temperatures and productivities than otherwise possible.
U.S. Pat. No. 6,479,424 discloses the preparation of unbridged species bis(2-(3,5-di-t-butylphenyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl) hafnium dichloride, bis(2-(3,5-di-t-butylphenyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl) zirconium dichloride, bis(2-(4-t-butylphenyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl) hafnium dichloride, and bis(2-(4-t-butylphenyl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl) zirconium dichloride which are used to produce propylene polymers.
Other references of interest include: 1) U.S. Pat. No. 6,034,022, (particularly example 17); 2) U.S. Pat. No. 6,268,444, (particularly example 2); 3) U.S. Pat. No. 6,469,188; and 4) EP 1 138 687, (particularly examples 8 and 9), and Olefin Polymerization Using Highly Congested ansa-Metallocenes under High Pressure: Formation of Superhigh Molecular Weight Polyolefins, Suzuki, et al., Macromolecules, 2000, 33, 754-759, EP 1 123 226, WO 00 12572, WO 00 37514, EP 1 195 391, U.S. Pat. No. 6,355,741, and Ethylene Bis(Indenyl) Zirconocenes . . . , Schaverien, C. J. et al., Organometallics, ACS, Columbus Ohio, vol 20, no. 16, August 2001, pg 3436-3452, WO 96/34023, WO 97/11098, U.S. Pat. Nos. 5,084,534, 2,852,501, WO 93/05082, EP 129 368 B1, WO 97/45434, JP 96-208535 199660807, U.S. Pat. No. 5,096,867, WO 96/12744, U.S. Pat. Nos. 5,408,017, 5,084,534, 6,225,432, WO 02/090399, EP 1 195 391, WO 02/50145, U.S. 2002 013440, WO 01/46273, EP 1 008 607, JP-1998-110003A, U.S. Pat. No. 6,562,914, and JP-1998-341202B2.
Another item of interest is an abstract obtained from the Borealis website that states:                Barbo Loefgren, E. Kokko, L. Huhtanen, M Lahelin, Petri Lehmus, Udo Stehling. “Metallocene-PP produced under supercritical conditions.” 1st Blue Sky Conference on Catalytic Olefin Polymerization, 17.-20.6.2002, Sorrento, Italy, 2002. “mPP produced in bulk conditions (100% propylene), especially at elevated temperature and under supercritical conditions, shows rheological behaviour indicative for small amounts of LCB in the polymer. This is a feature that can be utilized to produce mPP with enhanced melt strength under industrially meaningful conditions.”        